Radio broadcast selecting and distributing system



E. E. CLEMENT RADIO BROADCAST SELECTING AND DISTRIBUTING SYS'I'H FiledFeb. 29, 1924 3 Shana-Shut 1 umijueu Exammr E. E. CLEMENT RADIOBROADCAST SELECTING AND DISTRIBUTING SYSTEM Filed Feb. 29, 1924 3Sheets-Sheet 2 LEW M} IF .JW-J

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25o. pgp l w Patented Dec. 11, 1928. v UNITED STATES i 2 erasu PATENTOFFICE.

EDWARD E. CLEMENT, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO ED-WARD F. COLLADAY, OF WASHINGTON, DISTRICT OF COLUMBIA,

RADIO BROADCAST SELECTING AND DISTRIBUTING SYSTEM.

Application filed February 29, 1924. Serial No. 695,991.

My invention relates to systems of radio broadcast distribution, and hasfor its object to enable the subscribers in an organized system toselect individually the stations from which they desire to receive,while concentrating all the complicated apparatus necessary for suchselection at one or more central points, thus reducing the receivingapparatus at the subscribers stations to a minimum. The presentinvention is of the nature of an improvement over that described andclaimed in my prior applications filed February 9, 1924, Serial Nos.691,820, 691,821, and 691,822.

The problem presented is solved in the present case as follows:Modulated waves from a distant station are received, amplified, anddistributed to the subscribers from acentral station, using wiredcircuits, preferably existing telephone lines. The apparatus at thecentral station is adapted to receive waves at any frequency desired, totransform said frequency and to convey the modulations over thesubscribers lines at one standard frequency, made low enough forefiiciency of transmission, while remaining super-audio. To eii'ect thisfrequency transformation, the heterodyne principle is employed,providing local oscillators at the central station, and combining theiroutputs with incoming waves in such manner as to produce a beat wave.which is then delivered to the subscribers lines after detection, in theform of unidirectional pulsating current. Where there are severalsubscribers on one line, as on a telephone party line, it is desirableto adopt a corresponding number of standard beat frequencies. which maybe for example 257cc, 377cc, and 53700. Distribution to the No. 1subscribers on all party lines would then be on say, 257cc, distributionto No. 2 subscribers would be on 37700, distribution to No. 3subscribers on 53100, and so on.

I shall illustrate and describe herein very simple apparatus forcarrying this invention into efi'ect, with the understanding thatinstead of the manual switching apparatus shown, automatic apparatus, orso-called semi-automatic, may be employed, and that I consider them as apart of my invention.

My invention is illustrated as to one form of embodiment in theaccompanying drawings, in whichig. 1 is a simplified diagram showing theessential elements of the system.

Figs. 2 and 3 are detailed diagrams showmg modes of coupling to theantenna and to the oscillator circuits respectivel Fig. 4 is a diagramshowing t e same elements as Fig. 1, but with more detail.

Fig. 5 is a detail showing one manner in which the main tuning condenserand the selector switches for antenna and oscillator are coupledmechanically for conjoint selective operation.

Fig. 6 is a detail of the local signalling circuits at the centralstation, with the main or B battery bridged.

Fig. 7 shows the telephone switchboard with line terminals and one cordcircuit, and should be read together with Fig. 4.

Referring to Fig. 1, G represents in general a central station and S thesubscribers station. At the central station, 1, 2 and 3 are antennacircuits broadly tuned for three different bands of frequencies, notoverlap ping. 4, 5 and 6 are three separate couplers having theirsecondaries connected in series in the circuit 78, which also includes aload coil 9 and one of a series of oscillator couplers, as to thesecondary winding thereof, 10, 11 and 12. 13, 14 and 15 represent theoscillators, each of which is tuned and adjusted to produce alternationsor oscillations at a particular frequency only. is a switch by which thecircuit 8 may be connected to any one of the secondary coils of thecouplers 10, 11, 12. AC is a tuning condenser which together with theinductance of the several coils 4, 5, 6, 9 and 10, renders the circuit78 resonant or in tune with the frequency it is desired to receive. Fromopposite sides of the condenser AC wires 16 and 17 pass respectively tothe grid 21 and the filament 20 of the detector tube DT. Wire 16includes the usual grid con- 95 denser 19, and a grid leak 18. Thefilament battery is shown at 23 and the plate bat-.

tery at 23". From the latter wire 24 extends to the subscribers stationS, the return wire 25 connecting with the filament 20 and the wire 17.

The operation of the system thus outlined is as follows: A subscriberdesiring a particular station, calls up the radio operator, whothereupon adjusts the condenser AC so as to tune the circuit 78 to thewave length of that station, and also adjusts the switch AS so as toconnect the proper oscillator coupling 10, 11 or 12, whereby to impose aheterodyning frequency on the circuit 78 that with the frequencyreceived from the antenna 1, 2 or 3, as determined by the tuning of thecircuit, will produce a suitable beat frequency in the circuit 1617.This of course results from the imposition of the two relatively highfrequencies on the circuit 716, 817, which includes the grid 21 and thefilament return. The plate circuit of the detector tube D1 is connecteddirectly to the subscribers line, which is thus really a part of theplate circuit, a high potential pulsating current being produced in theline. to which the subscribers receivers are made to respond. It is tobe particularly noted that with the arrangement shown in Fig. 1 alltubes, complicated tuning devices, antenna circuits, oscillators, andbatteries are at the central station, and there is nothing at thesubscribers station by way of apparatus except his simple broadcastreceiving instrument and a phone condenser if desired.

Fig. 2 shows one antenna circuit, 1, with a common primary 1 and aplurality of secondaries 1", leading to the different circuits 7-8 inthe exchange. Fig. 3 shows a similar arrangement of the oscillatorcircuit 13 and the coupler 10, one primary 10 being employed and anumber of secondaries 10 Referring to Fig. 4, which is to be readtogether with Figs. 7, 1, 2 and 3 are the antenna circuits, 4, 5, and 6the couplers, but in; stead of having these all in series in the circuit7S, they are adapted to be connected thereto singly and selectively bythe double pole switch AS. The oscillator circuits 13, 14, 15 areconnected as before through the couplers 10, 11, 12 by means of theselective switch AS. The circuit 7-8 terminates in a plug P, thearrangement of the tube DT, the batteries 23 and 23 and associated partsbeing the same as in Fig. 1. By means of the plug P the tube with itsantenna switches and oscillator connections can be connected throughjacks J with any of the lines having radio service in the exchange.

In Fig. 5 I have shown the condenser AC, and the two double poleswitches AS and AS all coupled together on a common shift, by means ofwhich the condenser may be set to the particular station called for, theswitch AS may be set to the contacts of the coupling of the antennacircuit 1, 2 or 3, which includes the frequency of the desired station;and finally the switch AS is thereby set for the oscillator whosefrequency combined with that for which the condenser AC is adjusted,will produce the constant or standard frequency beat wave which is to beput on the subscribers line. Since the parts connected to circuit 16-17,which is the grid circuit of the detector DT are all local at thecentral station, and their constants may be determined and fixed, I amable to make the combined operation of the condenser AC and the twoswitches accurate and exact. In order to compensate for possible slightvariations in the antenna circuits or in the oscillator circuits, whichwould require slight overthrow one way or the other in turning condenserAC, I may give the contacts of the switches AS and AS more width than Ihave shown in the drawing, making these contacts if desired as arcs.Various other changes may be made, without departing from the principlesinvolved, which is that of conjoint action, by means of which the tuningand connection of the two heterodyning sources are accomplished at thesame time and automatically. In connection with this, it should bestated that instead of using a manually operated cord circuit with aterminal plug P, I may use any desired form of automatic selector; andin place of using a manual knob for turning the condenser AC and with itthe arms of the switches AS and AS, I may use step by step mechanismcontrolled from a distance, either by the operator or by the subscriberwho desires to receive from a particular station. In either case, asuitable dial or impulse sender would be employed, or the equivalent, toturn a ratchet wheel attached in place of the knob to the end of theshaft of the condenser AC in Fig. 5.

In order that the radio operator may have supervision and control overthe connection of the cord circuit and plug P, with any line, I providethe cord with keys K-K. The key K is a listening key, by means of whichthe operator can connect her telephone across the cord and line, and thekey K is a ringing key whereby the operator may connect a ringinggenerator to the subscribers line and call him in the usual way or bymeans of any suitable and desired ringing device with which his stationmay be provided. In order that the telephone operators may know that aline is connected for radio, and in order that the line relay LR (seeFig. 7) may be cut off while the line is in use, I provide a batteryconnection 13 (Fig. 4) which may be either the main telephone batteryshown in Fig. 7, or a special battery, and a tone test BT of known type.IVhen the plug P is inserted in a jack J, the tip sleeve and ringcontacts, p, 7) and 7 come into conjunction with the jack contacts j, j,and 7' the first of which goes to the tip side of line 24, the second tothe sleeve side of line 25, and the third to the wire circuit 26 leadingto the cut-off relay CO, shown in Fig. '7, and to the test thimbles j ofall the multiple jacks of the same line. The tone test BT should be acharacteristic radio tone test, so that the operators will all know,when they get that test, that they are at liberty to plug in on thetelephone switchboard and ringthe wanted subscriber,

DIAN.

which can be done without stopping the radiophone receiving. Forenabling the subscriber to call in, a supervisory signal may be providedas in Fig. 6, to which the tone test BT must be added. In this case,allowance must be made for battery current in the line of suflicientamperes to work the supervisory relay SR, which controls the supervisorylamp SL. In Fig. 6, I have shown the battery 23, that is to say, theplate battery. as bridged across the cord conductors 1.6 and 17, withradio and audio choke coils 23, in the battery bridge. This is ordinarytelephone practice, in so far as the bridging of the battery isconcerned and for audio purposes is well known in the art, but I believeis novel and original with me in connection with a detector circuit, orfor the passage of super-audio currents. The action in the plate circuitwould be to cause oscillations to pass through the main line to thesubscriber, due to variance of potentials which cannot produce anyvariance in the current How in the battery bridge, owing to the chokecoils 23.

The arrangement of the plate battery 23" in Fig. 4 is in series, and theoperators listening key K may be designed to put her headphone inseries. The arrangement of the battery 23 in Fig 6 is in bridge or parallel, and in this case the operators head phone may be in parallel, ormay be connected in series as before.

All the switchboard circuits shown in Figs. 4, 6 and 7 as well as thesubscribers telephone circuit in Fig. 7, are standard lVestern ElectricNo. 1 circuits. Anyother standard and suitable telephone circuits may besubstituted, without departing from the scope of the invention.

In Fig. 7 I have shown two subscribers receiving instruments, one TRbeing a headphone with a variable condenser SC bridged across it in acord circuit which terminates ing a plug P adapted to cooperate with ajack J 2 connected to the line of the subscribers station S; and theother HR, be ing a cabinet instrument containing a wooden horn oramplifier h, and phone condenser SC if desired, and amplifyingapparatus, consistin either of tubes or other means which Will. enablethe modulated waves received from central to be detected, amplified andpropagated through the horn h.

In operation, the subscriber in this system desiring to receivemodulated radio waves from a particular station, calls up the radiooperator at the central ofiice, which he may do by moving the switchhookof his telephone up and down, to flash the signal lamp controlled by hisline relay LR on the telephone switchboard. This s'gnal lamp may have aduplicate included in its own circuit and located upon the radioswitchboard if desired, but for simplicity one signal lamp txaminer issufiicient. The telephone operator perceiving the lamp to fiash, reconizes a. radio signal and by means of suitable order circuits not shown,gives the number of the line to the radio operator, who thereupon plugsin with a plug as P in Fig. 4, and by means of K connects her telephoneand ascertains the subscribers wishes. The stations which may beselected by the subscriber may be designated either by numbers or bytheFr call letters. In either case, the condenser dial AC if such beused, may he graduated and marked with the letters and numbers of thesaid stations, and the operator by setting the condenser to the desiredstation will thereby automatically tune the circuit 1617, connect theproper antenna circuit 1, 2 or 3, and the proper oscillator 13, 14 or 15to produce standard heat wave for which the subscribers lines andreceiving circuits are adapted. By listening in on the plate circuitthrough the key K, the operator may sharpen the tuning, if desired.l/Vith the arrangement shown in Fig. 6 after the foregoing connectionshave been made, the subscriber may recall the operator b the flashing ofsupervisory lamp SL, it being supposed that the resistance of hisreceiver bridged across the line is suitable for this purpose. Recallsare for the purpose of changing the station from which program is beingreceived. If necessary to prevent undue shunting of the modulated wavessent out over the conductors 24-425, a radio choke coil may be insertedin the telephone branch at the station S. I have not considered itnecessary to show this, but I wish it understood that such expedicnts aschoke coils, condensers and the like, which are known in the art, are tobe applied wherever needed in the practical use of this system.

I claim:

1. A broadcasting system comprising the following instrumentalities:subscribers stations and a central station containing receivingapparatus with a tunable input circuit for selection of radiotransmitting stations, means for supplying heterodyning oscillations tosaid circuit, a wire line extending to a subscribers station, and adetector at the central station having its grid circuit connected tosaid tuned input circuit, and its plate circuit extended directly tosaid line, together with suitable receiving means at the subscribersstat-ion responsive to current undulations in said plate circuit.

2. A broadcasting system comprising the following instrumentalities:subscribers stations and a central station and wire linesinterconnecting them, switching terminals for said lines at the centralstation, and radio distributing means also at the central stationcomprising switching terminals adapted to cooperate with the lineterminal, a thermionic tube having its plate circuit connected to saidswitching terminals together with a suitable source of plate current,and a signal device in said plate cir cuit with means at a subscribersstation re- 5 sponsive to current changes in the plate circuit andadapted to control said signal.

3. A broadcasting system comprising the following instrumentalities:subscribers stations and a central station and wire linesinterconnecting them, switching terminals for mionic tube having itsplate circuit connected to said switching terminals together with asuitable source of plate current bridged across the plate circuit, andthereby bridged across the subscribers line, when switched forreceiving, a signal in series with and on the line circuit side of saidbattery bridge 52/5271 4 %/J;Jd 7 4 434 7 fl/J; 7 424 6 4 4/0 57 2'2 4 J0 0 J 6 and means at a subscribers station adapted to produce changes insaid line circuit and plate circuit current and thereby operate saidsignal. I

4. In a radio broadcasting system, a central distributing stat-ion,subscribers stations connected therewith by wire lines, radio receivingapparatus at said central station with means for selecting differentprimary transmitting stations, means for supplying amplifying current, adetector tube connected to receive said waves with the amplifyingcurrent, and means to extend the plate circuit of said tube to a wireline thence to the subscribers station with means at said stationresponsive to modulated unidirectional pulsating current impulses insaid plate circuit and line.

In testimony whereof I hereunto atfix my signature.

EDWARD E. CLEMENT.

